This application relates generally to gas turbine engines and more specifically to a cooled turbine blade having a trailing edge cooling circuit with several unique features.
Conventional gas turbine engines include a compressor, a combustor and a turbine assembly that has a plurality of adjacent turbine blades disposed about a circumference of a turbine rotor. Each turbine blade typically includes a root that attaches to the rotor, a platform and an airfoil that extends radially outwardly from the rotor.
The compressor receives intake air. The intake air is compressed by the compressor and delivered primarily to the combustor where the compressed air and fuel are mixed and burned. A portion of the compressed air is bled from the compressor and fed to the turbine to cool the turbine blades.
The turbine blades are used to provide power in turbo machines by exerting a torque on a shaft that is rotating at a high speed. As such, the turbine blades are subjected to myriad mechanical stress factors. Further, because the turbine blades are located downstream of the combustor where fuel and air are mixed and burned, they are required to operate in an extremely harsh environment.
Hot burnt fuel-air mixture is expelled from the combustor and travels downstream to the turbine assembly, including the plurality of turbine blades. Each individual turbine blade includes a leading edge and a trailing edge, a pressure side and a suction side. The leading edge extends upwardly from the platform along the airfoil and is the first edge to contact the hot burnt fuel-air mixture as it travels through the turbine assembly. The trailing edge is substantially parallel to the leading edge and is located downstream of the leading edge. The pressure side is a concave surface that extends between the leading edge and the trailing edge. The pressure side directs the hot burnt fuel-air mixture along the turbine blade toward the trailing edge. The suction side is a convex surface, adjacent to the pressure side. The suction side also extends from the leading edge to the trailing edge. Various internal cooling circuits are disposed between the pressure side and the suction side.
As the hot burnt fuel-air mixture travels past the leading edge, along the pressure side, and past the trailing edge, a temperature associated with the individual turbine blades increases resulting in increased stress within the turbine blade. A cooling fluid, e.g. an airflow, is delivered to each individual turbine blade via the various internal cooling circuits sandwiched between the pressure side and the suction side of the turbine blade. The cooling circuits direct cooler compressed air bled from the compressor up through the root of the turbine blade and throughout the airfoil to cool the turbine blade.
One known cooling circuit technique directs airflow from the root radially outwardly toward the trailing edge. This cooling circuit receives an airflow from an opening disposed in the root of the turbine blade and feeds the airflow from an inlet passage radially outwardly through a feed passage. A known transition from the inlet passage to the feed passage includes a sharp corner that inhibits airflow from the inlet passage to a lower portion the feed passage. This may create a hot spot, i.e. an area of higher stress, within the turbine blade.
One known feed passage includes at least one barrier extending a length of the feed passage and a plurality of cross-over holes disposed along the length of the barrier. Known cross-over holes direct the airflow toward both a plurality of teardrop shaped protrusions downstream of the barrier and a plurality of openings disposed between each of the teardrop shaped protrusions. The plurality of teardrop shaped protrusions are disposed along the trailing edge of the turbine blade and direct airflow upward along the trailing edge and out of the turbine blade.
Known barriers includes cross-over holes of varying size. A width between adjacent cross-over holes also varies along the length of the barrier. This variation in size and position of the cross-over holes can cause a non-uniform airflow through the feed passage. This may result in additional hot spots, i.e. areas of higher stress, within the turbine blade. Further, known positioning of the cross-over holes in relation to the teardrop shaped protrusions may also have a detrimental effect on the cooling efficiency of the airflow.
As such, it is desirable to provide a turbine blade including a trailing edge cooling circuit that is optimized to reduce the effects of the mechanical stress factors, improve air flow throughout the airfoil and maximize cooling efficiency.